1. Field of the Invention
This invention relates generally to fluorescent-lighting fixtures; and more particularly to novel electrical connecting systems for such fixtures.
2. Prior Art
The working parts of fluorescent fixtures, sometimes called "luminaires", constitute a difficult field characterized by extremely high sales volumes, low unit prices and extremely competitive pricing. These factors magnify differences of a fraction of a cent in component cost, assembly time, and inventorying or shipping efforts--and relatively small differences in installation convenience--into major concerns.
Traditionally transformers or "ballasts" for fluorescent fixtures were made with protruding electrical leads for individual connection to the fixture wiring by installation personnel. That work was done, either in the fixture factory or (especially for replacement ballasts) in the field, using individual, manual splicing techniques such as wire nuts.
The evident labor-intensiveness of such procedures, as well as inventory ramifications, have led the industry in recent years to introduce the so-called "leadless" ballast. Such a ballast has an associated electrical half-connector, which is sometimes (but not necessarily) mounted to or in the wall of the ballast housing.
The ballast-associated half-connector terminates all or nearly all the leads from the electrical windings which are within that housing. A mating half-connector terminates the leads from lamp sockets that form part of the luminaire, so that the electrical-connection part of the installation process may be reduced to simply plugging one half-connector into the other.
In most leadless-ballast configurations the two incoming power leads are also wired through this same connector. In some configurations those two leads, or for instance special sensing or control-signal leads, may be handled separately.
It is important to note--as will be more fully appreciated later--that strain-relief provisions for each lead, at both sides of the connector, are essentially a requirement in the fluorescent-lighting industry as they are required for approval by safety-certifying organizations such as the Underwriters Laboratories.RTM.. Strain relief is more important in this field than in most consumer-product industries because ballasts are very heavy and luminaires are typically mounted overhead; if the mechanical connections of a ballast are not completed properly, the wiring provides a last-ditch backup against potentially severe injury or property damage below.
Most typically all the male terminals or contacts are held in one of the two half-connectors--usually and preferably the ballast-associated half, but sometimes the fixture-associated half. Correspondingly the female contacts are held in the other half-connector (i.e., usually but not necessarily the fixture-associated half).
In principle male contacts can be used for some leads and female contacts for other leads within each half-connector, but this is not popular in the industry. At any rate each contact typically is held within its own respective throughhole, formed fore-to-aft through the half-connector.
A favored type of contact, particularly for the female contacts, in leadless-ballast connectors is the well-known rolled sheet-metal variety that has outward-biased retaining tangs. During contact installation (forward insertion from the rear of the half-connector) the tangs are compressed radially inward--generally into line with the cylindrical rolled body of the contact--allowing the contact to pass forward through a cylindrical inner surface of an inner flange or ledge, molded as part of the interior surface of the through-hole.
After passing through the flange, the tangs spring outward radially so that their tips can bear longitudinally against the annular surface of the flange or ledge: the annular ledge thus serves as a tang stop. In this way the tangs and ledge cooperate to prevent the contact from escaping rearward from its through-hole.
Contacts of this configuration can be used for the male pins as well. In the interest of economy, however, some commercial configurations instead simply use the bared ends of the electrical leads--i.e., bared wire ends--as the male contacts.
A male contact of this type is extremely attractive because it is essentially free of material cost. The very slight additional length of wire substitutes entirely for a rolled or other formed male pin, thus eliminating entirely the cost of a formed pin; and the bared-wire-ends technique adds at most a minor smoothing of the cut tips.
The wires whose ends are bared may be held in the half-connector through-holes using adhesive, or slug locks as described in the parent patent documents identified earlier, or by sideways-driven wedging devices, or by ultrasonically fusing material of the half-connector with insulation adjacent to the bare wire ends, or through other fastening techniques.
Unfortunately, the economic appeal of such bared-wire-end contacts is not fully met in practice, for they do not engage the female contacts as reliably. The reason is that the bare-end contacts are typically less rigid than, and lack the bullet nose or profile of, the rolled sheet-metal contacts.
During contact installation or handling, before mating of the two half-connectors to install the ballast, the tips of the bared wire ends are somewhat more susceptible to bending away from a nominal straight-in-line position relative to the through-hole. Such bent, untapered ends fail to pass smoothly into the female contacts. A solution would be particularly useful in this case, though even formed pins can misalign.
The tantalizing economies of the bare-wire-end contact place a premium on effective but inexpensive provisions for reinforcing or recentering the male-contact tip or otherwise guiding it into its respective female contact. Heretofore no such effective but inexpensive provision has appeared.
Standard female contacts do have a forward-facing bell intended to help capture male-contact tips that are only slightly off-center. The bell diameter, however, is severely limited--by the requirement that the bell, as well as the rest of the female contact, must pass through the small-diameter internal flange or tang stop.
Because the diameter of the bell must be so small, while it may be adequate for the small amount of out-of-line deformation likely to occur in a relatively strong rolled-metal metal pin it is inadequate for the greater deformation that often occurs in a relatively weaker bared-wire-end male contact. The overall result is that the standard-size bell is ineffective: the contacts fail to engage.
In theory a larger-diameter centering bell can be provided if the female contact is inserted rearward into its through-hole from the front of the half-connector, rather than forward from the back. This technique, however, requires threading each wire, too, rearward through the hole, in advance of the contact--and only after that making the connection of the opposite end of that wire with its socket, winding, etc.
This threading operation is very time consuming, and the associated sequence of operations (socket or winding connection after threading) is relatively awkward. Thus use of a large-bell female contact would generate added costs-- possibly even high enough to negate the savings of the bared-wire-end contacts--and is unacceptable.
Therefore full enjoyment of the potential economy of bared-wire male pins has not been possible heretofore. As can now be seen, important aspects of the technology used in the field of the invention are amenable to useful refinement.